Ytterbium(II) amides and crown ethers: addition versus amide substitution

NMR spectroscopy and ion pairing: Measuring and understanding how ions interact

“…The value of the Overhauser measurements is nicely illustrated by an NMR study on the crown ether stabilized salt, [K(18-crown-6)(NPh 2 )] [16b]. The solid-state structure for this salt has been determined [19] and reveals a π-interaction between one of the aniline rings and the potassium atom, as indicated in 3. The measured diffusion data in THF solution for this salt are given in Table 3 along with D values for Ph 2 NH and the free crown ether.…”

“…If the diffusion characteristics of the anion and cation can be measured separately (easily done if the anion contains either a suitable 19 The ease with which one can recognize differences in ion pairing, using this approach, is demonstrated by the data in Table 2 In a relatively nonpolar solvent such as CDCl 3 , the two D (and r H ) values are almost identical, indicating almost complete ion pairing. In methanol solution, the two D values are very different, suggesting little or no ion pairing.…”

“…NMR spectroscopy and ion pairing 623 Macchioni and coworkers [9,20] in a series of papers have made specific use of 19 F, 1 H HOESY (heteronuclear Overhauser spectroscopy) measurements on transition-metal salts, and have shown that this is a viable method for placing the fluorine-containing anions relative to their cations, in three-dimensional space. However, this approach is quite general.…”

“…Specifically, one finds a substantial, multinuclear ( 1 H, 7 Li, 19 F, 31 P, 195 Pt) literature concerned with the use of pulsed field gradient NMR methods to measure diffusion constants [3][4][5][6], and the subject has been reviewed several times [7,8]. In the classical pulsed field gradient spin-echo (PGSE), Fig.…”

Structural Elucidation of tmeda‐Solvated Alkali Metal Diphenylamide Complexes

“…It consists of a planar K 2 N 2 ring (sum of endocyclic angles: 360°); however, due to the larger size of potassium, its coordination sphere can accommodate an additional donor atom (hence each K atom is five-coordinate). Supplementary stabilisation by K···π-arene interactions appears minimal [shortest K···C separations are 3.1936 (13) Only three other donor complexes of potassium diphenylamide have been crystallographically characterised, namely the solvent-separated 18-crown-6, [82] dimeric thf [61] and polymeric dioxane [62] solvates ( Figure 6). Clear structural similarities exist between 3 and the aforementioned Figure 6.…”